Most
of the ocean floor
is a huge, dark, nearly
flat area called the
Abyssal Plain.

The sea floor is a huge flat area.
It lies at depths of about 4000 to 6000 meters below the
surface of the ocean. It is called the Abyssal
Plain. Sea floor spreading occurs here, which means
that there is volcanic action and a mid-ocean ridge where
some of the lava has cooled. There are also isolated
volcanic mountains called sea mounts, and some black
smokers, but most of this area is flat and featureless.

To
a surface dweller
the abyssal plain is an intimidating
environment.
At best, light
penetrates the ocean
for only about 200
meters (less
than 600 feet).
Below that there is
a twilight zone of
very faint light,
and by 1000 meters
the ocean, and the plain
below it, is in
total
darkness. It is
also cold, the
temperature being
only a little above
freezing. The
pressures from the
weight of the water
above the abyssal
plain are enormous,
and can easily crush
a submarine.

There are no
photosynthesizers on
the abyssal plain
because no light
gets down
there. So what
do the animals eat?

Well, the main problem for
the animals living
on the abyssal plain
is finding something
to eat. There
is no light,
therefore there are
no plants, which
cannot
photosynthesize in
darkness.
Although there are
some sulfur using
bacteria at the
black smoker vents,
these vents are
rare, and could not
support all the
animals living on
the abyssal plain.

The
life forms on the
abyssal plain are
dependent on the
life forms living in
the light far above
them. Many
deep sea animals
swim up towards the
surface at night to
find food, and can
then become prey for
animals that live
still deeper.
Many abyssal plain
animals stay in the
depths and make do
with what they can
find
there. Tiny
particles of organic
matter slowly drift
downward and nourish
the animals living
on the abyssal
plain. These
animals are able to
live on very little
-- they have low
metabolic rates
(they are cold, and
chemistry happens
slowly in the cold)
and may not move
around much.
We do not know about
their growth and
reproduction.

Food reaches the
abyssal plain by
drifting down from
the sun-lit surface. As the
food drifts past
many animals on its
way to the ocean
floor, much of it
gets eaten, and the food that
gets to the bottom
is made up fine
particles, tiny bits
of decaying plant
matter and tiny
scraps of dead
animals. The
benthic (bottom
dwelling) animals live on and
in the fine
particles that
silently rain down
on them.
Sometimes these
particles get
stirred up: they are
tiny and light, and
easily wafted up
into the water
again. The
particles settle very
slowly, and so are
called "marine
snow" when they
hang suspended in
the water.

Occasionally a huge
animal, such as a
dead whale, may fall
down onto the abyssal
plain. The
bottom dwelling
animals can detect
food from a great
distance, and they
come to eat as much
as they can.
Because of their low
metabolism, the
animals can go a
long time between
meals, months,
perhaps, or even a
year or longer.

The
abyssal plain is
surprisingly rich in
life forms. As
this environment has
changed very little
over the history of
life, there has been
plenty of time for
the animals to adapt
to the conditions
there.
The animals may be
widely scattered,
but they exhibit a
surprising
diversity. The
life forms include
zooplankton,
sponges, sea
anemonies, starfish,
sea cucumbers, sea
pens, octopi and crinoids,
as well as many
smaller animals,
such as copepods and
nematodes.
There are many
different species,
even though the
number of
individuals in each
species may be
small.

The
animals in this
biome have many
unique
adaptations.
Many of them are
bioluminescent,
which means that
they can emit
light.
Sometimes this is
done by providing a
sheltered
environment for
bioluminescent
bacteria that live
in the animals,
sometimes the
animals generate the
light themselves. These
lights are used for
many purposes, such
as for attracting
mates or becoming a
lure for prey.
Some animals have
enormous eyes that
can detect even the
very faintest light,
or huge
mouths.
Some of these
animals have
fantastic shapes
that are different
from the forms of
animals that live in
the lighted world.

The animals that
live on the abyssal
plain are well
adapted to their
environment.
Could they move to
more shallow depths
in the ocean?
Remember that the
ocean has many
inhabitants, like
these abyssal plain
dwelling rattail
fish, and
each
inhabitant occupies an
environmental
niche. By
adapting to a niche
an animal develops
ways of living that
give its species an
advantage in eating
certain food sources
and occupying
certain
spaces. This
means that the
resources in the
ocean are being used
and newcomers would
have to compete for
them. As the
bottom dwelling
animals have adapted
to occupying niches
on the ocean floor,
they are less fitted
to move into other
niches which might
require new
adaptations.

However, if there
were some sort of
global catastrophe,
such as a huge
meteor strike that
killed many surface
dwellers, some of
the abyssal plain
animals might move
into new or vacant
niches. They
are a reservoir of
living creatures
that might yet
inherit the earth.